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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108498] [11/12/13 Regression] ppc64 big
 endian generates uninitialized reads with -fstore-merging
Date: Tue, 24 Jan 2023 17:46:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108498

--- Comment #24 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Eric Botcazou from comment #23)
> > The C/C++ FEs since r9-6625-gbec1da64aec26a490 turn some array initiali=
zers
> > into strings.
>=20
> Ouch.  I'm not sure that's worthwhile if the arrays are not byte-aligned.

They actually are byte aligned.
What happens is basically we have first some INTEGER_CST byte-sized store,
then a STRING_CST store and then an INTEGER_CST store of just a few bits.
So, the conditions for merging the first INTEGER_CST with the STRING_CST are
met,
string_concatenate is set, everything is contiguous and so the bit store at=
 the
end
is merged in (in the testcase there are some other stores in between too, a=
ll
INTEGER_CSTs).
In the end we got a group with 71 bits with byte aligned start and we just
store 64 bits and leave those 7 uninitialized.=